for question (a):
obviously (you'll see this from the diagram) ABC forms a triangle. all the angles of a triangle add up to 180 degrees. you are given two angles in the triangle. how would you find the third?
for question (b):
again, a diagram is important here. once you have a diagram, all you need to find the required angles is the Alternate Segment Theorem. see what it says here (it's a little more than half way down the page)